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<h1><a name="SECTION0018500000000000000000">
16.5 <tt class="module">crypt</tt> --
         Function to check <span class="Unix">Unix</span> passwords</a>
</h1>

<p>
<a name="module-crypt"></a>  
<p class="availability">Availability: <span
 class="platform">Unix</span>.</p>

<p>
This module implements an interface to the
<span class="manpage"><i>crypt</i>(3)</span><a id='l2h-3531' xml:id='l2h-3531'></a> routine, which is a one-way hash
function based upon a modified DES<a id='l2h-3529' xml:id='l2h-3529'></a> algorithm; see
the <span class="Unix">Unix</span> man page for further details.  Possible uses include
allowing Python scripts to accept typed passwords from the user, or
attempting to crack <span class="Unix">Unix</span> passwords with a dictionary.

<p>
Notice that the behavior of this module depends on the actual implementation 
of the <span class="manpage"><i>crypt</i>(3)</span><a id='l2h-3532' xml:id='l2h-3532'></a> routine in the running system. 
Therefore, any extensions available on the current implementation will also 
be available on this module.
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3530' xml:id='l2h-3530' class="function">crypt</tt></b>(</nobr></td>
  <td><var>word, salt</var>)</td></tr></table></dt>
<dd> 
  <var>word</var> will usually be a user's password as typed at a prompt or 
  in a graphical interface.  <var>salt</var> is usually a random
  two-character string which will be used to perturb the DES algorithm
  in one of 4096 ways.  The characters in <var>salt</var> must be in the
  set <tt class="regexp">[./a-zA-Z0-9]</tt>.  Returns the hashed password as a
  string, which will be composed of characters from the same alphabet
   as the salt (the first two characters represent the salt itself).

<p>
Since a few <span class="manpage"><i>crypt</i>(3)</span><a id='l2h-3533' xml:id='l2h-3533'></a> extensions allow different
  values, with different sizes in the <var>salt</var>, it is recommended to use 
  the full crypted password as salt when checking for a password.
</dl>

<p>
A simple example illustrating typical use:

<p>
<div class="verbatim"><pre>
import crypt, getpass, pwd

def login():
    username = raw_input('Python login:')
    cryptedpasswd = pwd.getpwnam(username)[1]
    if cryptedpasswd:
        if cryptedpasswd == 'x' or cryptedpasswd == '*': 
            raise "Sorry, currently no support for shadow passwords"
        cleartext = getpass.getpass()
        return crypt.crypt(cleartext, cryptedpasswd) == cryptedpasswd
    else:
        return 1
</pre></div>

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